用Collections.sort方法对list排序有两种方法
第一种是list中的对象实现Comparable接口，如下：
/** * 根据order对User排序*/public class User implements Comparable<User>{private String name;private Integer order;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getOrder() {return order;}public void setOrder(Integer order) {this.order = order;}public int compareTo(User arg0) {return this.getOrder().compareTo(arg0.getOrder());} } 测试一下：public class Test{public static void main(String[] args) {User user1 = new User();user1.setName("a");user1.setOrder(1);User user2 = new User();user2.setName("b");user2.setOrder(2);List<User> list = new ArrayList<User>();//此处add user2再add user1list.add(user2);list.add(user1);Collections.sort(list);for(User u : list){System.out.println(u.getName());}} }
输出结果如下ab
第二种方法是根据Collections.sort重载方法来实现，例如：
/** * 根据order对User排序*/public class User { //此处无需实现Comparable接口private String name;private Integer order;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getOrder() {return order;}public void setOrder(Integer order) {this.order = order;} } 主类中这样写即可(HastSet——>List——>sort进行排序)：public class Test {public static void main(String[] args) {User user1 = new User();user1.setName("a");user1.setPrice(11);User user2 = new User();user2.setName("b");user2.setPrice(2);Set<User> Hset = new HashSet<User>();Hset.add(user2);Hset.add(user1);List<User> list = new ArrayList<User>();list.addAll(Hset);Collections.sort(list,new Comparator<User>(){public int compare(User arg0, User arg1) {return arg0.getPrice().compareTo(arg1.getPrice());}});for(User u : list){System.out.println(u.getName());}}
输出结果如下：
ab
默认为升序，，将。return arg0.getOrder().compareTo(arg1.getOrder()); 改为：return arg1.getOrder().compareTo(arg0.getOrder()); 就成降序的了。
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